Sealer or primer composition of an acrylic polymer having adhesion promoting groups and an epoxy resin

ABSTRACT

A sealer composition or a primer composition that is used for the repair of a painted or an unpainted metal substrate having excellent adhesion to the substrate that has as the film-forming constituents 1. AT LEAST 50 PERCENT BY WEIGHT, BASED ON THE WEIGHT OF THE FILM-FORMING CONSTITUENT, OF AN ACRYLIC POLYMER OF AN ACRYLIC ESTER THAT IS AN ALKYL METHACRYLATE OR AN ALKYL ACRYLATE IN WHICH THE ACRYLIC POLYMER HAS ADHESION PROMOTING GROUPS ATTACHED TO THE POLYMER BACKBONE; 2. AT LEAST 5 PERCENT BY WEIGHT OF AN EPOXY RESIN; AND 3. 0-40 PERCENT BY WEIGHT OF AN ORGANIC PLASTICIZER.

United States Patent Richard A. Sandstedt Flint, Mich.

Dec. 12, 1968 Dec. 14, 1971 E. I. du Pont de Nemours and Company Wilmington, Del.

Inventor Appl. No. Filed Patented Assignee SEALER 0R PRIMER COMPOSITION OF AN ACRYLIC POLYMER HAVING ADI-IESION PROMOTING GROUPS AND AN EPOXY RESIN 3 Claims, No Drawings Primary Examiner-Morris Liebman Assistant Examiner-L. T. Jacobs Attorney-Hiimar L. Fricke ABSTRACT: A sealer composition or a primer composition that is used for the repair of a painted or an unpainted metal substrate having excellent adhesion to the substrate that has as the filmiorming constituents l. at least 50 percent by weight, based on the weight of the film-forming constituent, of an acrylic polymer of an acrylic ester that is an alkyl methacrylate or an alkyl acrylate in which the acrylic polymer has adhesion promoting groups attached to the polymer backbone;

2. at least 5 percent by weight of an epoxy resin; and

3. 0-40 percent by weight of an organic plasticizer.

SEALER on PRIMER COMPOSITION OF AN ACRYLIC POLYMER HAVING ADHESION PROMOTING snows ANDAN EPOXY RESIN BACKGROUND OF THE INVENTION This invention isrelated to a coating composition, and more specifically to sealer and primer composition used as a subcoat in the repair of finishes on auto and truck bodies.

Sealer and primer composition are well known in the art, for example, Melamed U.S. Pat. No. 2,992,132, issued July 11, 1961, illustrates thermosetting primer coating compositions. Other coating compositions shown in Blake U.S. Pat. No. 2,949,445, issued Aug. 16, 1960, Hurwitz U.S. Pat. No. 2,954,358, issued Sept. 27, 1960 and Hankins et al. U.S. Pat. No. 3,037,006, issued May 29, 1962, illustrate coating compositions that can be used as sealer and primer compositions. However, these prior art compositions, while very useful, do not have the combination of properties, such as adhesion to unprimed metal and enamel or lacquer coatings along with rapid air dry properties, which are desirable for a sealer and primer composition.

The novel composition of the invention will adhere to an alkyd or acrylic enamel finish or to an unprimed metal substrate and air dries in a relatively short period to a tough, durable film. Moreover, a variety of topcoats have excellent adherence to the dried novel coating composition of this invention, such as, thermosetting acrylic enamels, alkyd enamels, lacquers of polymethyl methacrylate, nitrocellulose lacquers, and even coatings of polyvinyl chloride. These topcoats exhibit excellent weatherability, chip and crack resistance indicating that the novel sealer composition has excellent adhesion to the substrate.

SUMMARY OF THE INVENTION The liquid coating composition contains 50-50 percent by weight of film-forming constituents and a solvent for the filmforming constituents in which the film-forming constituents consist essentially of l. at least 50 percent by weight, based on the weight of the film-forming constituents, of an acrylic polymer consisting eswherein n is l to 2, R, R and R are each selected from the group of hydrogen, an alkyl group having 1-4 carbon atoms and an aryl group, R is either a heterocyclic group or a divalent aromatic radical;

2. at least 5 percent by weight, based on the weight of the film-forming ingredients of an epoxy resin of the following structural formula wherein n is an integer sufficient to provide the epoxy resin with a molecular weight of at least 20,000; R is a divalent aromatic radical; R,'R' and R are each selected from the group of hydrogen and an alkyl radical having 1-5 carbons atoms; R is an alkylene group having 1-5 carbon atoms; and

3. 0-40 percent by weight, based on the weight of the filmforming constituents, of an organic plasticizer.

DESCRIPTION OF THE INVENTION Preferably, the novel coating composition of this invention has a solids content of the film-forming constituents of about 10-20 percent by weight and the film-forming constituents consist essentially of 55-75 percent by weight of the acrylic polymer, 10-30 percent by weight of the epoxy resin and 20-40 percent of an organic plasticizer.

Theacrylic polymer used in the novel coating composition of this invention contains about 0-5 percent by weight of an a, B-ethylenically unsaturated monocarboxylic acid. Typically useful a, B-ethylenically unsaturated monocarboxylic acids used in the acrylic polymer are acrylic acid, methacrylic acid, crotonic acid and the like. Preferred are acrylic acid and methacrylic acid since these acids form high quality polymers.

The acrylic polymer contains about 50-99 percent by weight of an alkyl methacrylate ester or an alkyl acrylate ester or a mixtures of these esters. The alkyl group of the aforementioned esters contains l-8 carbon atoms and is of a lower alkyl monohydric alcohol. Typical esters used for the acrylic polymer are methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, octylmethacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, hexyl acrylate, 2- ethylhexyl acrylate and the like.

Up to 50 percent by weight of the acrylic polymer can be contributed by the monomers having adhesion promoting groups. Generally, these adhesion promoting monomers have sites of ethylenically unsaturation which can by polymerized into acrylic monomer backbone. One method of preparing these monomers is to react one of the aforementioned a, )3- ethylenically unsaturated monocarboxylic acids and a constituent containing an adhesion promoting group. Then this monomer is polymerized with the other acrylic esters to form an acrylic polymer. s

Typical monomers which provide adhesion promoting groups to the acrylic polymer are hydroxyaminopropyl methacrylate, aminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, 2- aminopropyl methacrylate, Z-aminoethyl methacrylate, t-butylamineothyl methacrylate, 2-(l-aziridinyl)-ethyl methacrylate, n-2-hydroxypropyl-methacrylamide and n2-hydroxyethylemethacrylamide.

The preparation of the hydroxy amino propyl methacrylate is disclosed in U.S. Pat. Nos. 2,949,383 and 2,949,445, both issued on Aug. 16, 1960, which are incorporated by reference.

The 3-amino-3-hydroxypropyl methacrylate is prepared by reacting methacrylic acid with 2( l-aziridinyl)ethanol.

The Z-aminopropyl methacrylate and Z-aminoethyl methacrylate are prepared by reacting methacrylic acid with ethylene amine and propylene amine respectively.

The following are examples of typical acrylic polymers having adhesion promoting groups suitable for use with this invention: 97/3-99/1 copolymer of methyl methacrylate/hydroxyaminopropyl methacrylate; /3/2 terpolymer of methyl methacrylate/methacrylic acid/B-amino 3-hydroxypropyl methacrylate; 50/50-99/1 copolymer of methyl methacrylate/diethyl-aminoethyl methacrylate; 75/25-99/1 copolymer of methyl methacrylate/2-aminopropyl methacrylate; 75/25/99/1 copolymer of methyl methacrylate/Z-aminoethyl methacrylate; 50/50-99/1 copolymer of methyl methacrylate/2-( l-aziridinyl)-ethyl methacrylate; 50/50-99/ 1 copolymer of methyl methacrylatelt-butylaminoethyl methacrylate; '50/50-99/1 copolymer of methyl methacrylate/dimethylaminoethyl methacrylate; 90/ -99/ 1 copolymer of methyl methacrylate/N-Z-hydroxypropyl methacrylamide; 90/10-99/ l copolymer of methyl methacrylate/N-Lhydroxy-ethyl methacrylamide.

One particularly preferred adhesion promoting group is provided by a monomer having the formula wherein m is an integer having a value of 2 to 3, R" is selected from hydrogen, methyl, ethyl. R is selected from C to C, alkylene groups, and R and R are selected from (1) separate groups selected individually from (a) hydrogen, phenyl, benzyl and C, to C alkyl groups in the case of R and (b) hydrogen and C to C. alkyl groups in the case of R", and (2) a single group selected from pentamethylene and tetramethylene which, together with the carbon atom to which the single group is attached, forms a carbocyclic group.

The aforementioned adhesion promoting monomer used in the acrylic polymer of this invention is prepared according to the procedure described in the aforementioned U.S. Pat. No. 3,037,006, the disclosure of which is incorporated by reference. An especially preferred embodiment of this adhesion promoting monomer used in the acrylic polymer of this invention is of the formula It will be apparent to those skilled in the art that this monomer can be referred to as (l) 3-(B-methacryloxyethyh- 2,2-penta-methylene-oxazolidine; (2) 3-(2-methacryloxyethyl)-2,2-spiro-cyclohexyl-oxazolidine; (3) MESO or (4) loxa-4-(2'-methacryloxy-ethyl)-4-azaspiro [4.5 decane.

' One particularly preferred acrylic polymer used in the novel composition of this invention contains about 90-99 percent by weight methyl methacrylate and about 1-10 percent by weight acrylic polymer and the novel coating composition of the invention are toluene, xylene, butyl acetate, acetone, methylisobutyl ketone, methylethyl ketone, butyl alcohol, and other aliphatic cycloaliphatic and aromatic hydrocarbons,

esters, others, ketones, and alcohols, such as are conventionally used in coating compositions.

About 0.1-4 percent weight, based on the weight of the monomers, of a polymerization catalyst is used to prepare the acrylic polymer. Typical catalysts are ditertiary butyl peroxide, cumene hydroperoxide, azobisisobutyronitrile and the like.

The epoxy resins useful for the sealer compositions of this invention are high in molecular weight. in general, they have the structural formula,

wherein,

n is an integer sufficient to provide the epoxy resin with a molecular weight of at least about 20,000, R, is a divalent aromatic radical; R R and R, are individually selected from the group of hydrogen and a C to C alkyl, R, is a C, to C, alkylene group. R, as shown above, can be a bisphenol A or a bisphenol F, both of which can be substituted. Bisphenol A is para, para-isopropylidene diphenol. Bisphenol F is 4,4'dihydroxydiphenyl methane. Suitable substituents include C to C, alkyls, halogens such as chlorine, bromine, and fluorine, and C to C, alkoxy groups.

The preferred epoxy resin is the reaction product of epichlorohydrin-bisphenol A which has the structural formula,

where n is as defined above.

Epoxy resins used with this invention must be high enough in molecular weight so that the films formed are flexible and nonbrittle; molecular weights of about 20,000 are generally sufficient. Higher molecular weights are preferred up to and beyond 200,000.

Plasticizers can be used in the coating composition of this invention to impart desirable properties to the coating such as epoxidized soya bean oil, oil-free and oil modified alkyds and polyesters, such as, polyorthophthalate esters, polyalkylene adipate esters or polyarylene adipate esters, benzylbutyl phthalate, dibutyl phthalate, triphenyl phosphate, 2-ethylhexylbenzyl phthalate, dicyclohexyl phthalate, diallyl phthalate, dibenzyl phthalate, butylcyclohexyl phthalate, mixed benzoic acid and fatty oil acid esters of pentaerythritol, poly(propylene adipate) dibenzoate, diethylene glycol dibenzoate, tetrabutylthiodisuccinate, butyl phthalyl butyl glycolate, acetyltributyl citrate, dibenzyl sebacate, tricesyl phosphate, toluene ethyl sulfonamide, the di-2-ethylhexyl ester of hexamethylene diphthalate, di(methylcyclohexyl)phthalate. One preferred plasticizer is benzylbutyl phthalate.

One preferred composition has a film forming solids content of about -20 percent by weight and about 50-75 percent by weight of the forming constituents, of an acrylic polymer of 90-99 percent by weight, based on weight of the acrylic polymer of methyl methacrylate and l-l0 percent by weight of 3-(Z-methacryloxyethyl)-2,2-spirocyclohexyloxayolidine; l0-30 percent by weight of an epoxy resin of epichlorohydrin para,para-isopropylidenediphenol having a molecular weight of about 20,000-200,000; -40 percent by eight of benzylbutyl phthalate.

Pigments are used in the novel coating composition of this invention in the amounts of 0. l-50.0 percent pigment volume concentration, preferably, a pigment volume concentration of about 0.3-6.0 percent is used for a sealer composition. Primer composition preferably have a pigment volume concentration of 20-45 percent. Examples of the great variety of pigments which are used in the novel coating composition of this invention are metallic oxides, preferably titanium dioxide, zinc oxide, iron oxide and the like, metal hydroxides, metal flakes, chromates, such as lead chromate, sulfides, sulfates, carbonates, carbon black, silica, talc, china clay, organic dyes and lead, iron blues, organic reds, maroons, and the like, organic dyes and lakes, etc.

The novel compositions of this invention can be applied to a variety of substrates, for example, metal, glass, plastics, such as styrene copolymers of styrene, and the like, by any of the usual application methods, such as spraying, dipping, brushing, flow coating and the like. These coatings can be air dried or baked at about 93-150" C. to increase the drying rate. The resulting coating is about 0.1-5 mils thick, preferably, l-3 mils thick and can be sanded, if desired, to improve smoothness.

The characteristics of the novel composition of this invention that make the composition useful particularly in refinishing or repairing the finishes of autos and trucks is the rapid air drying characteristic and excellent adhesion to bare or treated metal, or metals previously painted with alkyd or acrylic enamels. Also, the novel composition can be highly pigmented or used as a clear sealer coat. After application of the novel composition only a short air dry period is required before a topcoat can be applied. Topcoats of lacquer and enamels have excellent adherence to the novel dried sealer or primer coat of this invention and have excellent durability and weatherabilit The following examples the invention.

EXAMPLE 1 Polymer A solution is prepared for use in a sealer composition as follows:

Portion l is a charged into a reaction vessel equipped with a stirrer and a condenser and the ingredients are heated to 72 C. and held at 85 C. Portion 2 is premixed and charged into the reaction vessel and the ingredients are refluxed for about 4-5 hours at 80 C. until the reaction mixture reaches a Gardner Holdt viscosity of about V-Z measured at 25 C. The resulting polymer solution has a polymer solids content of about 40 percent and polymer A has a composition of MMA/MESO in a weight of ratio of /5.

A sealer composition is prepared by blending the following ingredients:

Portion l Parts By weight Polymer A solution (40% solids) 967.8 i. 1. h (58%1" dioxide pigment dilperled in polymer A solution) 540.0

Portion 2 Ethylene glycol monoethyl ethe l,256.2 Toluene l,8l3.2 llopropanol 1,904.8

Portion 3 Butylbenzyl phthalate I7 I I Epoxy resin solution (40% polymer solid: in methyl ethyl ketone having a Gardner Holdt viscosity at 25' Portion l is charged into a sand mill and ground to a 0.5 mil fineness. Portion 2 is premixed and charged into the mixer containing Portion l and thoroughly mixed. Portion 3 is then added and the composition is thoroughly mixed to give a sealer composition that has a viscosity of 27 seconds in a No. 7 Parlin cup measured at 25 C. 1

The above sealer composition is sprayed onto five suitably primed steel panels coated with polymethyl methacrylate lacquer, five suitably primed panels coated with a thermosetting acrylic enamel and five steel panels in which there is a strip of untreated steel and the remainder of the panel is coated with a primer and a thennosetting acrylic topcoat which illustrates a typical substrate which has been repaired by conventional techniques. in each case, about a 0.5 mil tick coat is applied to the panel and air dried for about 35-45 minutes. in each case, the adhesion of the coating composition to the substrate is excellent. Adhesion of the sealer is determined by applying a strip of scotch tape to the coating, smoothing the tape to firmly adhere to the coat and then removing the tape. in case case, none of the sealer is removed indicating excellent adhesion.

Each of the above panels is lightly sanded and a coating of a conventional polymethyl methacrylate lacquer is applied and air dried. in each case, the lacquer has excellent adhesion to the sealer as determined by the aforementioned test.

EXAMPLE 2 A pigment dispersion which is to be used in a sealer composition is prepared by blending the following ingredients:

7 8 Portion 1 PM y s Each of the above panels is lightly sanded and a coating of a conventional polymethyl methacrylate lacquer is air dried. in Polymer A solution 40% solids-prepared in each case, the lacquer has excellent adhesion to the sealer as determined by the aforementioned test. Toluene 180.0 Magnesium silicate pigment 8L7 Bsryte: pigment l52.3 Titanium dioxide pigment 152.0 6&8 EXAMPLE 3 Finely divided silica 165.2 6mm Bhck mm mo The sealer compositions prepared in examples I 2 are field tested on autos which are sub ected to conventional use PM 2 and weathering. in each case, the coating did not crack, chip or peel and retained its adhesion to the substrate, even after P I no 40 0 long periods of use and severe weathering. The following table z i'x shows the various types of original finishes over which the Tom homo 15 sealer composition of example i or 2 is applied, a finish tops il sati fie W" he i r i s e es dred- TABLE Auto Sealer comnumber Original finish position Finish topcoat 5 Thermosetting acrylic enamel 6 -do g Polymethyl methacrylate lacquer Thermosetting alkyd melamine enameL. Example 1. Air dry alkyd enamel.

... .do Thermosetting acrylic enamel.

doIIIII Spot repair enamel prepared according to Example 1 o! 5.5. 491,815, filed Sept. 30, 1965.

1); Polymethyl methacrylate lacquer Example 2. Air dry alkyd enamel.

11 'lhermosetting alkyd melamine enamel .do Textured block polyvinyl chloride finish (root of a truck).

Portion l is charged into a sand mill and ground to a 0.5 mil 1 claim:

fineness. Portion 2 is then thoroughly mixed with Portion l. The resulting pigment dispersion has a pigment volume concentration of about percent.

A sealer composition is formed by blending the following ingredients: v

The above ingredients are charged into a reaction vessel and thoroughly mixed. The resulting sealer composition has a viscosity of 27 seconds in a No. 7 Parlin cup at 25 C.

The above sealer composition is sprayed onto 5 suitably primed steel panels coated with polymethylmethacrylate lacquer, 5 suitably primed panels coated with a thermosetting acrylic enamel and 5 steel panels in which there is a strip of untreated steel and the remainder of the panel is coated with a primer and a thermosetting acrylic topcoat which illustrates a typical substrate which has been repaired by conventional techniques. in each case, about a 0.5 mil thick coat is applied and air dried for about -45 minutes. in each case, the adhesion of the coating composition to the substrate is excellent.

Adhesion of the sealer is determined by applying a strip of scotch tape to the coating, smoothing the tape to firmly adhere to the coat and then removing the tape. In each case, none of thesealeris removed indicating e cellent adhesion.

l. A liquid coating composition that can be air dried comprising 10-20 rcent by weight of film-forming constituents and a solvent or saidconstituents in which the f lm-forming constituents consist essentially of 1. about -75 percent by weight, based on the weight of the film-forming constituents, of an acrylic polymer consisting essentially of 90-99 percent by weight of methyl methaicrylate, and correspondingly, l-lO percent by 40 weight of 3-(2-methacryloxyethyl)-2,2-spiro-cyclohexyl oxazolidine;

wherein R is selected from the group consisting of T/Ha sufficiently large to provide the epoxy resin with a molecular wei t of about 20,000 to 200,000;

3. about 20-40 percent by weight, based on the weight of the film-forming constituents, of a phthalate ester plasticizer. 2. The coating composition of claim 1 in which the plasticizer is butyl benzyl phthalate.

31. A metal substrate coated with a dried coalesced layer of the composition of claim 1.

i 0 i 1 i mg omTEo STATES PATENT oemoe QERTEWQATE F (IQREQTWN Datei 7 December 1 1-, 1971 Patent No. UQSQP. 3 6275 779 Invento Richard A Sandstedt It is certified that error appears in the above-idefitifie patent and that said Letters' Patent are hereby corrected as shown below:

E" "'71 @laim 1 column 8, line 55, after the formula ($11 the following should he added and -CH- and n is a positive integer Signed and sealed this 25th day of pr 1972.

(SEAL) Attest:

EDWARD M.FLJL'TGHhJR J1?a ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. AT LEAST 50 PERCENT BY WEIGHT, BASED ON THE WEIGHT OF THE FILM-FORMING CONSTITUENT, OF AN ACRYLIC POLYMER OF AN ACRYLIC ESTER THAT IS AN ALKYL METHACRYLATE OR AN ALKYL ACRYLATE IN WHICH THE ACRYLIC POLYMER HAS ADHESION PROMOTING GROUPS ATTACHED TO THE POLYMER BACKBONE;
 2. AT LEAST 5 PERCENT BY WEIGHT OF AN EPOXY RESIN; AND
 3. 0-40 PERCENT BY WEIGHT OF AN ORGANIC PLASTICIZER.
 2. about 10-30 percent by weight, based on the weight of the film-forming constituents, of an epoxy resin having the following structural formula wherein R9 is selected from the group consisting of sufficiently large to provide the epoxy resin with a molecular weight of about 20,000 to 200,000;
 2. The coating composition of claim 1 in which the plasticizer is butyl benzyl phthalate.
 3. A metal substrate coated with a dried coalesced layer of the composition of claim
 1. 3. about 20-40 percent by weight, based on the weight of the film-forming constituents, of a phthalate ester plasticizer. 